Neuronal activity will be recorded from rat substantia nigra and nucleus locus coeruleus to determine the effects of amphetamine and related agonists and antagonists of dopamine and norepinephrine on presynaptic function of catecholaminergic nerve cells. Of special interest will be whether these various agents of known neurochemical action produce alterations in the firing rates or patterns of catecholaminergic cells, and whether such agents affect the terminals of these neurons, as measured by their excitability to direct electrical stimulation. Electron microscopic examination of the substantia nigra will be undertaken with the aim of describing and categorizing the three-dimensional morphology of various inputs to the substantia nigra. Of speical interest will be the three dimensional structure of dendritic sites where catecholamines might be released, identified by 5-hydroxydopamine labeling, accumulations of synaptic vesicles and a synaptic junction between dendrites. Evidence for structural damage following chronic amphetamine administration will be sought in a continuing study of neostriatum where such damage has been reported at the light microscope level.